Dial up to a domain server is a few chapters in the book.
I think I see where you are going here. You want to avoid the 4 or more chapters in the books about setting up dial in services in Windows Servers.
Remember that this is one very small text box so I'll summarize as much as I can then suggest you go back to the Windows Server Administrator books for the hard core parts.
Again, you see folk think this stuff should be easy and just a few steps for what you asked, it's many chapters in the books.
1. Install the modem folk will dial into.
2. Setup remote access in Windows Server.
That's the short version. This is the how to forum so any more depth and you need a consultant or call Microsoft.